Conventionally, for example, in a radar mounted on an aircraft, in many cases, an array antenna apparatus is used which transmits radio-frequency pulse signals (hereinafter referred to as “RF pulse signals” in some cases) from a plurality of antenna elements. The RF pulse signals are reflected by an object, and the radar receives the reflection signals by the antenna elements of the array antenna apparatus, thereby detecting the object.
In general, an array antenna apparatus includes a plurality of antenna units, and is configured to execute transmission/reception via a plurality of antenna elements on an antenna unit by antenna unit basis. Each antenna unit supplies RF pulse signals, which are generated by RF pulse signal generation circuits, to the respective antenna elements. The RF pulse signal generation circuit is provided for each antenna element, and includes an amplifier circuit (power amplifier circuit) which is composed of an FET (field-effect transistor).
Conventionally, the RF pulse signal generation circuit includes a switching circuit which controls the drain voltage of the FET. By this switching circuit, the rise and fall of the RF pulse signal are controlled, and the response speed characteristics, which are necessary for high-speed transmission/reception of the radar, are realized. Here, since the high-speed switching circuit employs a plurality of FETs, the circuit configuration is complex. In addition, since a large high-voltage current flows in the drain of the FET, which constitutes the power amplifier circuit, a capacitor with a large capacitance is used as a peripheral circuit.
The RF pulse signal generation circuit is provided for each antenna element. Thus, as a result, the circuit scale of each individual antenna unit becomes relatively large. Hence, for example, in the antenna apparatus for use in a radar mounted on an aircraft, since the mounting space and weight are limited, a challenge lies in how to realize reduction in circuit scale of each individual antenna unit. In addition, there is a case in which the radar changes, based on an operation mode, the number of antenna elements which are control objects. In the conventional RF pulse signal generation circuit, since the drain voltage of the FET is constant, there is a case in which the output of the RF pulse signal becomes unstable when the number of antenna elements was changed. Thus, there is also a challenge in how to realize stabilization of output characteristics of the RF pulse signal in accordance with the number of antenna elements.